Water Value and Sustainable Use in the American SW
Mark E. Grismer
megrismer@ucdavis.edu
Hydrologic Sciences and Biological & Agricultural Engineering
1 Shields Ave, UC Davis
Davis, California USA 95616

Abstract
As elsewhere in the world, anticipated population growth in the next 50 years,
climate change and reduced surface water availability, water “productivity”, or water use
efficiency (WUE) must continue to improve in the American Southwest. Beyond the
intrinsic value to life, water takes on additional value as food and fiber, fisheries andecosystem benefits that are linked such that emphasis of one over the other benefit often
results in losses neglected in the past. For exa mple, development of upstream water
storage exchanges downstream fisheries and ecosystems benefits for crop production,
while reservoir evaporation losses further reduce possible downstream resource values.
Unlike WUE improvements in the municipal sector, possible through metering andtechnological changes in flow devices and washing appliances, improved WUE in crop
production is hampered by unidentified achievable water use targets. In terms of wateruse, the dominant crops in the Southwest are alfalfa and sudangrass hay and cotton lint
production. The water use characteris tics, average planted areas and yields, and water
values are examined for these crops in Arizona, California and Idaho to determine
possible target WUEs and assess possible on- farm water savings in the region based on
actual production information from 1988-2000. Field -based WUEs of 1.7, kg/ha- mm foralfalfa and sudangrass hay and pima cotton, and 2.1 kg/ha-mm for upland cotton lint
production appear to be practical target values from which to determine appropriate wateruse. Based on FAO #56 estimated and yield-based water use for these three crops,
possible water savings of up to 50% exist with the greatest water savings potential indesert regions where current water values as hay or lint crops are low relative to otherregions. Such high water savings in the desert region are unlikely and targets of 20-30%
corroborated by research trials, are more likely. The greatest water values and least
possible water savings occur in the southern San Joaquin Valley, CA where the
combination of relatively high ET and some rainfall occur. This research is a starting
point for assessing water use/savings at the field scale for hay and cotton productions andshould be extended to other crops. Additional work may also be required considering
water savings at the district scale associated with the water distribution systems.

Keywords: alfalfa hay, cotton, water use, water conservation, water value

1Introduction
The inextricable link between water and life is readily apparent in the competition
and associated conflict surrounding water resources and its quality throughout the world.
As population centers expand, this competition is becoming ever more keen andproblematic with respect to meeting basic human needs while maintaining the very
habitat upon which we depend and develop our food and fiber resources. Freshwater
withdrawals, storage or degradation in one part of a basin for development of agricultural
or municipal resources results in loss of downstream resources associated with fisheries
and possible environmental (e.g. habitat, water purification) benefits associated withriparian zones or wetlands. While the cost of developing upstream infrastructure in order
to translocate in time and space water resources for other beneficial uses may be offset inpart by the value developed there from, downstream losses in resource values associatedwith water purification, aesthetic benefit and fisheries are generally neglected. For
example, evaporation of water from upstream reservoirs that may provide a recreational
benefit, while returning to the hydrologic cycle, result in loss of water use for agriculture
and cities, as well as in-stream beneficial uses downstream. There is no “use” of water in
upstream areas, for either resource development or as a waste stream carrier, which does
not result in losses in value downstream. What remains is for society to determine where
to gain the most “water value” (or “productivity”) from limited water resources for[presumably] the greatest public good. Indeed, the United Natio ns and Ministerial
Declaration at the 3rd World Water Forum in Kyoto (2003) recognized the basic human“right” to water and that “to ensure a sustainable water supply of good quality, we should
protect and use in a sustainable manner the ecosystems that na turally filter, store andrelease water such as wetlands, forests and soils” (article 24). Further, noting that water
is essential for rural development, “we should make every effort to reduce unsustainable
water management and improve the efficiency of agricultural water use” (article 19).
Society worldwide is grappling with possible solutions or changes in water resources
paradigms to balance beneficial uses for all people as populations grow.
In many developed countries, annual freshwater withdrawals have alreadystabilized or fallen, despite ever increasing populations, resulting in less water use percapita, or greater water value per capita. The decreased water use per capita, or increased
efficiency is largely due to increased municipal water conservation. In contrast to
improving agricultural water use efficiency, municipal water conservation is more readily
achievable through application of technological improvements in low-flow devices,
reduced water use by washing appliances and the possibility of water metering. In
developing countries, freshwater withdrawals continue to grow with increasing
populations and agricultural development such that water use or value per capita is moreor-less constant. For example, the ratio of annual national gross domestic product (GDP),an indicator of overall economic well-being, to that of annual water withdrawals can beviewed as a measure of “water productivity”. Figure 1 illustrates how this ratio has
grown for the USA during the latter half of the past century and for Hong Kong during
the past 40 years based on federal estimates of GDP and water withdrawals (Gleick,2004). With the exception of the economic depression period after 1929, and the war
period growth in the mid 1940s, “water productivity” in the USA from 1900 – 1980
remained more-or- less constant as water withdrawals kept pace with population growth
and agricultural development in some ways similar to the present condition in developing2

countries. Water withdrawals in the USA leveled during the 1980s, such that present
water productivity has been increasing with population growth; a similar, though more
recent history and trend, is evident in Hong Kong. As has occurred nationally andinternationally, increased “water productivity” in the American southwest has not comeabout without some difficulty and conflict at many levels. In the following, examples ofdiffering scales and impacts are considered to illustrate some of the debate currently
underway in the region.
As in much of the world, water resources development in California and theColorado River basin of the arid southwest was directed at diverting streamflows intostorage for municipal or agricultural use without consideration of downstream losses, or
actual new water value developed from the new infrastructure versus that lost in
downstream benefits. The following examples help set the stage for assessin g, or
determining the value associated with water conservation and how it might be achievedin agricultural production so as to continue improving “water productivity” to better servea growing population with fixed water resources.
a) Lake Powell on the Colorado River – This is the upper basin reservoir designed toenable the upper basin states to meet the downstream discharge requirements of
the lower basin states (see Figure 2). Completion of the 171 m tall dam in 1963
enabled the reservoir to fill by 1980 to a volume of 33.3 km3 (27 000 000 ac-ft)
with a surface area of approximately 681 km2 (266 mi2). The lake isapproximately 298 km in length and there is approximately 3140 km of shoreline
with 96 major side canyons. Average annual evaporation is estimated at 2.5-3% of
the volume, or approximately 1 km3 /yr (860 000 ac- ft). At the time of
construction environmental groups decried loss of the picturesque and historic
Glen Canyon for a reservoir considered unnecessary or wasteful of precious waterin the southwest. This debate was rekindled during the recent 2001-2005 drought
period during which much of Glen Canyon was once again exposed as thereservoir declined to a small fraction of its full volume. Recreational boatinginterests around Lake Powell are adamant that the Lake serves a broad purpose
and tourism value that alone justifies its continued operation. In opposition,
environmental groups underscore the continued recreational value of the Glen
Canyon region to hikers, rafting and archeologists, but of perhaps greater value isthe possibility of recovering the significant evaporation water losses. The annual
evaporation from Lake Powell is sufficient to supply the annual water need of alarge metropolitan area, one-third of the annual irrigation water requirement of theImperial Valley, more than half of the 1944 USA-Mexico treaty obligation ofwater delivery at the border, and all of the surplus water taken by California .
Debate continues to rage concerning the “water value” of the reservoir.
b) Millerton Lake on the San Joaquin River – Friant Dam, completed in 1942 forstorage of 0.64 km3 (520 500 ac-ft) irrigation water to be delivered to some 416
000 ha of the southern San Joaquin Valley; the most productive agricultural
region in the world . The 319-foot high dam is 40 km northeast of Fresno, in the
shadow of the Sierra Nevada Mountains. The recent federal district court
settlement in September, 2006 from more than 18 years of litigation, will result in
release of 0.21 km3 (170 000 ac-ft) into the San Joaquin River for stream
rehabilitation and restoration of historic Chinook salmon runs at a cost of some3

$800 million, $330 million of which is to come from farmers. Salmon runs prior
to construction of the dam were said to be so abundant that the fish were used forhog feed. This unprecedented settlement between federal agencies, farmers andenvironmental groups appears to usher in a new era of better cooperation forwater resources in the San Joaquin Valley, though the downstream fisheries
benefit remains unclear as yet.
c) Hetch Hetchy Reservoir on the Tuolumne River – The O'Shaughnessy dam
created Hetch Hetchy Reservoir on the main stem of the Tuolumne River in Hetch
Hetchy Valley of the southern Sierra Nevada. The original dam was a 95 m highgravity-arch concrete dam completed in 1924 and raised to the current height of
131 m in 1947. The reservoir, with a capacity of 0.44 km3 (360 360 ac-ft), is
supplied primarily by snowmelt from an 1175 km2 (459 mi2 ) watershed locatedentirely within Yosemite National Park. The reservoir is managed by a San
Francisco Bay area public utility that has paid $30 000/yr since 1923 to lease thereservoir area in the National Park from the federal government. It is the drinking
water supply for some 2.4 million people in the San Francisco Bay area, whileproviding roughly 20% of its power needs. Hotly contested at the time of its
creation by John Muir, the reservoir covers the “second Yosemite Valley”,
considered a national treasure by many. Initial estimates of roughly $500 million
to remove the dam and replace the San Francisco water supply downstream areconsidered high, but considerable public support in the Bay area has developed.
Restoration of the Valley would create a new precedent for dam removal on the
grounds of aesthetic or moral value alone.
d) Tule Lake Water District – In the northeast corner of California and southern
central Ore gon large shallow lakes and wetlands existed prior to conversion toagricultural production some 80 years ago through diversion and storage ofKlamath River flows supplying the lake/wetland system by the federal
government. One such historic lake area was Tule Lake. Collapse of the
California north coast salmon fisheries in the past five years resulted in an
unanticipated mandated reduction of 0.12 km3 (100 000 ac-ft) in irrigation water
deliveries in 2001 from the Tule Lake water district to local farmers. This sudden
reduction in water deliveries resulted in subsequent drying of Tule Lake fromgroundwater extractions by 2005, idling of nearly 10 000 ha of farmland and lossof approximately $43 million in agricultural production for the 2001 production
year. The north coast salmon fishery remains tenuous and was declared eligiblefor disaster relief funds of $25 million, far short of the $81 million requested, inAugust, 2006. The value of the exchange of agricultural production inland withfisheries production at the coast is unclear in part due to other factors (e.g.
logging) affecting the fisheries, however, continued decreased irrigation water
deliveries are anticipated as part of the salmon recovery planning.
All four examples above illustrate paradigm shifts in allocation of water resources forbenefits not previously considered during the early to mid 20 th century period of dam
construction in the American southwest. Three of the four examples involve exchange of
irrigation water resources for anticipated, though to some degree unproven, downstream
fisheries benefits. The cost to agriculture alone of this exchange range s from roughly$0.35/m3 at Tule Lake to $1.57/m3 in the San Joaquin Valley. This range encompasses

4the water cost to recover Hetch Hetchy Valley of roughly $1.12/m3 . While each example
has specific nuances particular to the local, there appears to be no clear water cost/value
principle that might better guide society’s acceptance of such exchanges. [In some cases,changes in water resource project water availability associated with global warming may
drive reductions in agricultural water deliveries.] If water presently provided irrigatedagriculture is to be reduced, what volumes of water can be practically expected fromwater conservation efforts before crop yields are significantly diminished, and at whatcosts? If yields losses cannot be avoided are there other regions in which the crop
production can occur with smaller or no yield losses? Developing answers to thesequestions at the farm scale is the focus of this paper. Improving water distribution systemefficiencies at the district scale is beyond the scope of this paper, but an important overall
consideration.
However “water productivity” is characterized, it is clear that water use inagricultural production must become more efficient in order to meet the demands ofgrowing populations. Unlike water conservation programs in municipal areas whereclearly identifiable water use target values can be developed, no clearly identifiable
pragmatic water use efficiencies or water values are readily available for agricultural
production. Herein, drawing on research conducted primarily in California, but
applicable across the southwest USA, is an attempt to develop a rationale, or determine
water use efficiencies and water values for three crops grown in the southwest havingsome of the greatest gross water demand (see Table 1). Alfalfa hay, sudangrass hay andcotton lint production are selected not only because of their overall high water need in thesouthwest region, but because they also represent multi- year and annual crops in whichyield is generally evapotranspiration (ET) dependent when not soil moisture limited, anda more complex flowering crop in which yield is less dependent on ET.

Water Use Efficiency Studies
As a perennial crop having nearly complete canopy coverage, alfalfa hay
production is the dominant water use in the western states. Sudangrass hay, though anannual crop with greater heat and salinity tolerance is similar to alfalfa hay in terms of
production methods and water use characteristics. Ultimately, alfalfa hay is used for
cattle or dairy production and may be considered a resource for these industries. The
water use characteristics of alfalfa have been studied intensively (e.g. see Guitjens, 1990)
and efforts have been directed at determining appropriate crop production functions fordifferent areas, or to assess the effects of limiting water applications on hay yield.
Water production functions, often used by agricultural economists to estimate thewater use needed to generate the greatest economic returns to the grower, ideally relate
crop yield (Y) and crop water use (ETc), though some have related Y to applied water(AW). From a plant physiology perspective, under non-stress conditions the function
Y=f(ETc) is linear with a positive slope referred to as the crop water- use-efficiency(WUE). When using the dry matter yield of harvestable alfalfa, Y=f(ETc) should have anegative yield intercept, due to non-harvestable root development, and a maximum yield
point associated with the maximum ETc. Since Y=f(ETc) is linear, WUE is independentof ETc (Guitjens, 1982) and instead depends primarily on the plant’s CO 2 assimilation5

capacity (e.g. Asseng and Hsiao, 2000) or C13 /C 12 ratio (Saranga et al., 1998), hence
photosynthetic efficiency, or plant type (e.g. C3, C4, or leguminous).
By definition, WUE is constant for particular plant species and values in the rangeof 16-18 kg/ha - mm have been measured for alfalfa hay using lysimeters in Idaho (Fortier,
1940; Hill et al., 1982; and Wright, 1988) and Nevada (Guitjens, 1982; and Hill et al.,1982) and CO2 assimilation techniques in Central California (Asseng and Hsiao, 2000).
Asseng and Hsiao (2000) noted that alfalfa hay WUE is less than that reported for nonlegumes, but similar to that of other legumes such as soybeans. The lower WUE foralfalfa may be attributed to its partial allocation of carbon for symbiotic nitrogen fixationas compared to that for non-legumes. Little information is available regarding thesudangrass hay Y=f(ETc) relationship. Though this relationship is expected to be similar
to that for alfalfa, sudangrass is more salt-tolerant, capable of substantial osmotic
adjustment (Li et al., 1993), and as a non-legume should result in this relationship having
a somewhat greater WUE, and smaller yield intercept. Grismer and Bali (2001) and
Jensen (1995) measured and estimated, respectively, a sudangrass Y/ET c ratio of 15.6kg/ha-mm for production in the Imperial Valley during the period 1995-98. Grismer andBali (2001) however, noted that their ratio was low by about 15% due to salinity- induced
yield losses (Maas and Hoffman, 1977) suggesting a non-salinity stress WUE~18kg/ha mm. Based on estimated water use values, Grismer (2001b) determined a WUE of 20.7kg/ha-mm for sudangrass in the San Joaquin Valley. Figure 3 provides an example of thelinear Y=f(ETc) relationship for alfalfa hay production in the Sacramento and San
Joaquin Valleys of California based on estimated water use (Grismer, 2001a); note thatthe slope or WUE is equivalent to 18.7 kg/ha- mm and the negative intercept corresponds
roughly to less than a single hay cutting.
When relating alfalfa yield to AW rather then ETc, the initially linear function
reaches a maximum yield and either levels off, or decreases with increasing AW as aresult of excess water application beyond accumulated ETc. Slopes of the linear portionof the curve, measured using seasonal field plot (Tovey, 1963; Peterson, 1972; Donovan
and Meek, 1983; Frate et al., 1988; Rechel et al., 1991; and Guitjens, 1996) and line
source (Sammis, 1981; Hill et al., 1982; Smeal et al., 1991; Grimes et al., 1992; andHanson, 1996) experiments in the western states, range widely (10-25 kg/ha-mm).
Coincidentally, the average ratio from these studies (Y/AW=17.4 kg/ha-mm) is the sameas WUE=Y/ET c as cited above and is within the generally-accepted range of 15-20 kg/ha mm (Doorenbos and Kassam, 1979). Smaller Y/AW slopes (10-13 kg/ha- mm) are foundin desert regions (e.g. Erie et al., 1981; Donovan and Meek, 1983; Ottman et al., 1996;
and Ottman, 1999).
Cotton lint or seed WUE studies have had varied results reflecting the difficulties
in determining values consistent across the range of conditions encountered in the field(Grismer 2001c). Plant physiologists and others have been evaluating the range in cotton
genotypic variation in order to select for greater WUE characteristics (e.g. Gerik et al.,
1996; Saranga et al., 1998 & 1999; and Leidi et al., 1999) for both arid and elevated CO2
atmospheric conditions. For example, Gerik et al. (1996) found that cotton boll weight
was independent of cultivar (among six tested) and water stress, but that cultivars had
significantly different vegetative production, and bolls/ha production. Ayars et al. (1993)
and Hamdy et al. (1993) identify the sensitive growth stages and long-term managementof saline water application to cotton.

6

Cotton lint WUE also appears to be affected by planting patterns (spacing andlocation relative to furrows), mulching, tillage conditions and irrigation scheduling.
Narkhede and Bharad (1994) found that two plants per hill on a 1.5m by 1.0m spacing
improved cotton WUE significantly over a single plant per hill, while Shelke et al. (1999)
found that seed cotton yield was not significantly affected by planting patterns unless
irrigation was reduced to approximately half of ETc. Singh and Bhan (1993) reported
that maize-stove mulch laid between cotton rows improved cotton WUE, while Jin et al.
(1999) found that furrow planted cotton combined with plastic mulch WUE by more than
50%. While improved tillage practices may increase soil moisture storage conditions (e.g.
no-till in Texas improved water storage and dryland cotton yield; Baumhardt et al., 1993),
tillage effects on cotton WUE are unclear. Conservation tillage under dryland growing
conditions in Texas (Baumhardt and Lascano, 2000) and deep-ripping of vertisols inAustralia (Hulme et al., 1996) did not res ult in improved cotton WUE. However, in
Sudan Salih et al. (1998) found that cotton WUE increased by 25% when sub-soiling
vertisols as compared to disking cultivation methods. Effects of irrigation managementon cotton water use and soil salinity are summarized by Grimes and El-Zik (1982),
Hunsaker et al. (1998) and Ayars et al. (1999). Generally, cotton water use is greatest
during the peak blooming period and limiting soil- water availability at this time reduces
lint/seed yield, however this depends to some extent on the irrigation method. For
example, using drip irrigation Wanjura et al. (1996) found that cotton lint WUE increased
when delaying early season irrigation while providing sufficient water during theblooming stage. Stone and Nofziger (1993) reported increased cotton WUE through useof more widely–spaced (every other) furrow irrigation. Similarly, Sethi et al. (1995)
found that cotton WUE decreased with increasing soil wetness treatments and El- Awad
(2000) found that WUE was greater when furrow irrigating at three-week intervals ascompared to two-week intervals. Cotton water use from shallow water tables may reduce
short-term irrigation water needs (e.g. see Ayars, 1996; Hutmacher et al., 1996 and Soppe,
2000), but depends on shallow groundwater salinity and is of limited value if dense soil
layers are present (Cohen et al., 1995).
As briefly summarized above from plant physiology studies, cotton seed/lint
WUE is affected by a wide range of factors. This variability is also reflected in cotton
lint yield -water use (LY/ETc ) ratios determined from several recent studies summarized
by Grismer (2001c) in Table 2. This table focus es on more recent studies as new cotton
cultivars continue to be developed (as noted above) and soil- water manage ment practices
improve. Generally, WUE = LY/ETc values >3 kg/ha-mm appear possible under drip or
possibly furrow irrigation systems, far exceeding earlier estimates of 1.4-2 kg/ha- mm(Doorenbos and Kassam (FAO #33), 1979; Grimes, 1982 and Davis, 1983), even undermoderately high soil salinity conditions. Note that in Table 2 estimates of ETc
determined from micro-met station data (CIMIS and AZMET) and FAO #56 (Allen, et al.,1998) Kc values are much larger than study ETc values suggesting a significant
opportunity to reduce water applications based on these estimates without loss in yield(see Figure 4) regardless of the method of irrigation. Not surprisingly, the error inestimation of cotton water use diminishes as ETc increases to very high values where
actual ETc and estimated values appear to converge suggesting that more attention be
given to such estimates at low ETc conditions, thereby potentially reducing water
applications and improving net WUE.

7

Methodology
In order to determine target WUEs for hay and cotton lint production across thegreater southwest region, county-wide, or multiple county hay and lint yields, prices andestimated ETc were obtained from county data and micro-met station networks across thesouthwest and southern Idaho. Using actual production values incorporates the range ofclimate, soils and salinity stress effects on yield commonly encountered in the southwest(Grismer 2001a, 2001b & 2001c). No “adjustments” for irrigation application
efficiencies or leaching fractions were applied as these are not normally included in thedefinition of ETc and would unnecessarily obfuscate estimated Y=f(ETc), functions, aswell as limiting the meaningfulness of computed Y/ETc mean “target” values. While
Grismer et al., (1997) estimated water value ($/ha- m) based on the “cost” of yield loss
and water savings, here irrigation water value (IW$, $/ha -m) is taken as the product of
average county (region) market-year hay or lint price ($/Mg) and Y/IW (Mg/ha-m) forthe county (region) each year.
Results and Discussion
A linear Y=f(ETc) function suggests that irrigation water value as hay or lint
should be greatest in areas having matching rainfall contributing to crop ETc, however,this “matching investment” may be countered by the smaller available “ET energy” inthese areas and its greater variability, or investment “risk”. Grismer (2001a) found thatmaximum irrigation water values for alfalfa hay production in fact occur red in areas
having a combination of some rainfall and high available “ET energy”. Mean Y/ETcvalues (with their associated variance) may serve as “target”, or “reference” values towhich those resulting from alternative irrigation water strategies may be compared withina desired confidence level (variance). Tables 3 and 4 summarize the mean values andtheir variation of ETc, Yield/ETc and irrigation water values for hay and cotton lint
production, respectively, primarily in Arizona and California. Yield/ETc variations are
generally much smaller than water value variations and hay Yield/ETc variations are lessthan those of cotton, perhaps reflecting the myriad factors affecting cotton lint ascompared to hay production. Yield/ETc ratios and irrigation water values decline withincreasing ETc as shown in Figures 5 and 6, respectively, for hay production, and in
Figures 7 and 8, respectively, for cotton lint production. Note that sudangrass Yield/ETc
ratios are similar to that of alfalfa, though irrigation water values are considerably less.
Similarly, water values from upland cotton are roughly 10% less than that of pima cotton
lint production, though pima lint yields are 20-30% less than that of upland varieties.
Linear regression intercept values from Figures 5 and 7 are consistent with expected
WUEs for both crops, that is, about 18 kg/ha- mm for hay and 2.5 kg/ha - mm for cotton
lint production.
Both the tables and figures suggest that crop production in the high ET desert
regions do not generate the greatest return on water “investment” as compared to more
moderate ET conditions found in cooler areas inland or in some cases along the coast.
Conceptually, Yield/ETc should not be function of ETc, and if the desert area (high ET)data is separated, there is in fact no relationship between Yield/ETc and ETc for either
subset of data. From Tables 3 and 4, it is apparent that expected WUEs are only
approached in the San Joaquin Valley (or along the coast and LA where total planted8areas are relatively small). There appears to be an opportunity then to allocate less water
to the other areas without loss in yields and this volume of “saved” water can be
determined and compared to anticipated reductions in reservoir releases for agriculture.
Perhaps hay and cotton lint production in desert environments may not be tenable and thewater may have greater value in other applications. On the other hand, is it possible toincrease hay or lint yields in the desert areas to levels comparable to that found inland?
For example, in the Imperial Valley intense summer heat results in relatively low hay
yields but high water use, so it has been suggested that summer irrigations be reduced tosimply that necessary to maintain the hay stand but not achieve significant production.
How much improvement can be obtained and do other farm water management
techniques exist that enable expected WUEs to be achieved? If so, how much water“savings” might be expected?
For alfalfa and sudangrass hay production on heavy clay soils in the Imperial
Valley, Bali et al. (2001) and Grismer and Bali (2001) found that the “reduced runoff”
surface irrigation (a simplified volume-balance model approach to determining irrigation
cut-off time or distance developed by Grismer and Tod, 1994) resulted in greater hay
Yield/ETc ratios. In practice the methods requires measurement of a presumably nearly
constant onflow rate and a single measurement of surface water advance rate down thefield. During the three- year stud ies, the average alfalfa Yield/ETc ratio was increased
from an estimated Valley average of 8.9 to 15.2 kg/ha- mm. This latter value iscomparable to that obtained in high production regions of the southern San Joaquin
Valley (see Table 3). Correcting project hay yields for an estimated 30% reduction
associated with an average soil salinity of 6 dS/m (Maas and Hoffman, 1977) suggeststhat the reduced-runoff irrigation method resulted in a Yield/ETc ratio of nearly 21 kg/ha mm, a value similar to the maximum WUE expected for alfalfa hay. Similarly, a
Yield/ETc ratio of 15.5 kg/ha- mm was obtained for sudangrass hay production
approximately 15% less than expected WUE as a result of an estimated 15% salinitystress induced loss. Average seasonal water application was reduced by about 0.4 m, oran estimated 20% for sudangrass hay production and by 28% annually for alfalfa hay
through elimination of tail- water runoff. Improved Yield/ETc ratios were obtained in partfrom limited use of shallow groundwater by the stressed alfalfa crop during its first yearof production. These results from the reduced-runoff irrigation trials as well as thosefrom the drip and furrow irrigation trials under high soil- salinity conditions in the San
Joaquin Valley (see Table 2) suggest that greater attention be given to anticipated salinity
effects on hay and cotton crop coefficients, and subsequent estimations of applied water
depths. Moreover, the results suggest that significant water savings of 20-30% arepossible as compared to present irrigation methods in the desert regions for these crops if
lower yields are to be expected in desert production.
Allowing for potential depressed yields as a result of salinity stress as well as
pragmatic considerations of crop production, average water allocations (neglecting
rainfall) sufficient to achieve target WUEs of say 17, 1.7 and 2.1 kg/ha- mm for hay, pima
and upland cotton lint production, respectively, can be determined from average yields
and planted areas and compared to Yield/ETc presently obtained to determine potential
water savings at the farm level per county or area. Tables 5 and 6 summarize harvested
areas, yields and potential water savings for hay and cotton lint production, respectively,
as a result of improving area Yield/ETc ratios to the target WUEs above. Possible water9

savings appear to be substantial at the farm scale ranging up to nearly 50% of estimatedET (see Figure 9). It may be possible that crop coefficients are large for hay and cotton
crops under desert cultivation, or that desert production may simply result in less efficientwater use and regional planning for water allocations should be cognizant of this problem.
Improving Yield/ETc ratios for alfalfa hay and cotton lint production in the southern San
Joaquin Valley, partially a service area of Friant Dam, may result in a water savings 2.4
times the recently mandated water releases for in-stream fisheries. Similarly, possible
water savings in the Imperial Valley from hay and cotton production total nearly 19% of
its entire Colorado River allocation. On the other hand , the combined annual watersavings potential from the Imperial and southern San Joaquin Valleys for hay and cotton
production total just over the evaporation losses at Lake Powell.
Summary & Conclusions
Anticipated population growth, climate change and reduced surface water
availability will strain already overused water supplies of the American Southwest suchthat overall water “productivity”, or WUE must increase in the region. Agricultural
production is the dominant water user and public demand for fisheries and ecosystembenefits limits development of additional water storage. Past development of upstream
water storage has exchanged downstream fisheries and ecosystems benefits for crop
production in many cases, while reservoir evaporation losses further reduce possible
downstream resource values. Unlike WUE improvements in the municipal sector,
possible through metering and technological changes in flow devices and washing
appliances, improved WUE in crop production is hampered by unidentified achievable
water use targets at the farm level, and to a smaller degree at the irrigation/water districtlevel. In terms of water use, alfalfa and sudangrass hay and cotton lint production are thedominant crops in the Southwest. The water-use characteristics from research studies,average planted areas and yields, estimated water use and water values are examined forthese crops in Arizona, California and Idaho to determine possible target WUEs andassess possible on-farm water savings in the region based on actual production
information from 1988-2000. Field-based WUEs of 1.7, kg/ha- mm for alfalfa andsudangrass hay and pima cotton, and 2.1 kg/ha - mm for upland cotton lint production
appear to be practical target values from which to determine appropriate water use.
Based on FAO #56 estimated and yield -based water use for these three crops, possible
water savings of up to 50% exist with the greatest water savings potential in desert
regions where current water values as hay or lint crops are low relative to other regions.
Such high water savin gs in the desert region are unlikely and targets of 20-30%
corroborated by the research trials, are more likely. These results suggest that crop
coefficients may be large for these crops under desert cultivation, or that desert
production may simply result in less efficient water use. The greatest water values andleast possible water savings occur in the southern San Joaquin Valley, CA where the
combination of relatively high ET and some rainfall occur. Increasing WUE of the hay
and cotton crops in the desert regions would make water values as crops in these regions
more consistent with that of other water uses. This research is a starting point forassessing water use/savings at the field scale for hay and cotton productions and should
be extended to other crops. Additional work may also be required considering watersavings at the district scale associated with the water distribution systems.

10References
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13

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14

Table 1. The top ten crops in terms of water demands grown using CO River water inthe American southwest.
Consumptive Use (ha-m/yr) each year
Crop
2000
2001
2002
Average
Alfalfa hay
100019101594104128101914
28568
32430
34643
31880
bermudaSudangrass hay
19629
18495
17497
18540
12544
10415
9989
10983
sugar beets
10280
8592
9643
9505
wheat
Cotton lint
2379
5499
3766
3881
4035
3635
3832
3834
carrots
3369
3352
3415
3378
citrus
4013
2898
2666
3192
onions
2210
3017
3032
2753
Misc. field crops

15

Table 2. Recent cotton yield - water use studies around the world.
Location
Irrigation Method
Study
FAO
Lint
LY/ETcETc#56 ETc
Yield(kg/ha(mm)(mm)(Mg/ha)mm)
San Joaquin
Valley, CA(high salinity)

San Joaquin
Valley, CA(high salinity)

TurkeyArgentina

Texas

East Hebei Plain,
North China
Negev, Israel

Central Arizona

San Joaquin
Valley, CA

SJ Valley, CA(high salinity)

Drip irrig.- lysimeters
1998
1999
Sprinkler/furrow–
1997
1998
1999
Drip systems
1992
1993
Furrow systems
1992
1993
Furrow systems
1993
1994
Furrow systems
1991
1992
1993
Dryland (1992-95)
Clean tillage
Wheat residue
Furrow systems (1994)
No mulch
Plastic mulch
Drip systems (1994-95)
Full irrigation
Irrigation @ 50100% ET oLevel basin (1993-94)
Low frequency
Low-high-low freq.
High frequency
Drip systems (1993-94)
Early irrigation
Delayed, low freq.
Delayed, high freq.
Drip & Furrow(1993-94)

710
845

914
988

1.32
2.16

1.86
2.56

567
561
561

1005
914
988

1.16
0.62
1.23

2.04
1.12
2.19

549
691

1011
994

1.78
2.04

3.24
2.95

437
645

1011
994

1.40
1.50

3.20
2.33

834
899

?

1.16
1.21

1.39
1.34

1.68
1.92
1.95

2.29
3.87
3.09

736
495
631

?

200-300300?

0.29-0.51
0.37

1.51-1.66
1.22

506
426

?

0.85
1.13

1.67
2.62

491-566349-390?

---

2.1-3.4
2.1-3.4

1.14-1.32
1.38-1.52
1.25-1.47

1.32-1.55
1.47-1.63
1.41-1.64

1.46
1.59
1.46
1.23-1.55

2.36
3.33
2.42
1.53-2.03

1338
852-867889-894932-939
992
620
477
605
713-805992

16

Table 3. Estimates of mean alfalfa and sudangrass hay ETc, Yield/ETc and irrigationwater values (IW$) and their variability for production in Arizona, California andsouthern Idaho (from Grismer, 2001a & b).
ETc
Y/ETc
Y/ETc
IW$ IW$ C
1Region(mm) (kg/haCV
(USD/
V
mm)
(%)
ha-m)
(%)
Arizona – alfalfa
Lapaz
1979
9.04
6.83
945
15.7
Maricopa
1817
9.74
4.97
1082
12.3
Mohave
1892
8.77
10.2
963
9.61
Pinal
1812
9.71
9.15
1107
20.3
Yuma
1882
10.4
8.81
1078
16.4
California – alfalfa
NE Plateau
979
10.4
8.61
1344
22.5
N. Sacram. V.
951
11.7
7.87
1733
29.2
C. Sacram. V.
1066
13.7
5.46
1900
20.3
S. Sacram. V.
1145
12.5
7.07
2166
29.6
N. S Joaq. V.
1166
13.6
4.80
1931
19.0
C. S Joaq. V.
1220
14.9
7.68
2031
17.8
S. S Joaq. V.
1292
14.0
4.02
1861
16.9
C. Coast
971
19.3
6.39
2792
20.4
LA Basin
1105
17.2
5.87
2967
14.1
Rivers.-SB
1651
9.33
6.94
1420
18.1
N. Desert
1337
13.9
11.5
1187
17.7
Imperial V.
1657
7.91
8.57
1213
15.2
Idaho - alfalfa
S. West
882
14.0
7.48
1630
17.5
S. Central
788
14.6
6.49
1814
15.3
S. East
695
13.5
9.62
1789
19.8
California - sudangrass
C. S Joaq. V.
825
9.56
13.6
721
29.2
Rivers.-SB
1003
13.8
18.3
1202
23.5
Imperial V.
1054
12.5
18.4
1213
22.8
1
CV is the Coefficient of Variation = standard deviation/mean.

17

Table 4. Estimates of mean cotton lint ETc, Yield/ET c ratios and irrigation water values(IW$) and their variability (from Grismer, 2001c).
ETc
LY/ETc LY/ETc
IW$IW$Region(mm)(kg/
CV (%) (USD/CV
ha-mm)
ha-m)(%)
Arizona (Upland cotton)
Lapaz
1362
1.28
10.2
1870
8.56
Maricopa
1023
1.33
6.68
2111
12.5
Mohave
1034
1.27
17.8
1867
16.5
Pinal
1007
1.34
8.41
2180
16.3
Yuma
1035
1.38
13.1
2057
15.6
Arizona (Pima cotton)
Lapaz
1362
0.92
18.2
2094
20.4
Maricopa
1023
0.90
9.84
2244
17.4
Pinal
1007
0.90
13.2
2266
23.3
Yuma
1035
1.09
21.5
2507
27.8
California (Upland cotton)
C. Sacram. V.
656
1.73
28.5
3293
26.6
S. Sacram. V.
672
1.64
17.1
4821
49.7
N. S Joaq. V.
684
2.10
10.3
3777
15.3
C. S Joaq. V.
750
1.91
8.60
3411
10.9
S. S Joaq. V.
776
1.67
12.0
3038
5.99
S. Desert
990
1.34
19.6
2334
24.3
Imperial V.
1008
1.37
20.4
2384
35.3
California (Pima cotton)
C. S Joaq. V.
750
1.77
9.95
4172
13.6
S. S Joaq. V.
776
1.51
16.6
3500
9.57

18

Table 5. Average hay harvested areas, yields possible water savings through achieving
expected WUE.
Average
Water
State/Region Counties
Harvested Hay Yield Savings?
hectares(Mg/ha)(ha-m/yr)
Arizona - alfalfa
Lapaz
17 52317.9
16227
Maricopa
20 936
17.7
16243
Mohave
2610
16.6
2390
Pinal
6610
17.6
5134
Yuma
13 341
19.5
9805
California - alfalfa
NE Plateau
Lassen/ Modoc
24 427
10.2
9258
N. Sac. V.
Shasta/ Siskiyou
27 374
11.1
8159
C. Sac. V.
Butte/ Colusa/
17 068
14.6
Glenn/ Sutter/
3536
Tehema/ Yuba
S. Sac. V.
Sacramento/
16 427
14.3
Yolo
4991
North San
Contra Costa/
72 762
15.8
Joaquin V.
Merced/ San(N. SJV)
Joaquin/
17215
Stanislaus
C. SJV
Fresno29 452
18.2
4400
S. SJV
Kern/ Kings/
89 59718.1
Tulare20365
C. Coast
Monterey/ San
2363
18.7
Luis Obispo/ S.
0BarbaraLA Basin
Los Angeles
3543
19.0
0
Riverside/SBRiverside/ San
27 431
15.4
Bernardino
2640
N. Desert
Inyo
1544
18.6
375
S. Desert
Imperial
73 531
13.1
65179
Idaho - alfalfa
S. West(see footnote 1)
73 403
12.3
11632
S. Central(see footnote 2)
102 917
11.5
11478
S. East(see footnote 3)
168 819
9.41
23883
California - sudangrass
N. SJV
Merced/ Stanis.
1158
7.88
419
Riverside/SBRiverside/ San
Bernardino
2943
13.8
563
S. Desert
Imperial
27115
13.1
7621
1
Ada, Adams, Boise, Canyon, Elmore, Gem, Owyhee, Payette, Valley & Washington counties.
2
Blaine, Camas, Cassia, Gooding, Jerome, Lincoln, Minidoka, & Twin Falls counties.
3
Bannock, Bear Lake, Bingham, Bonneville, Butte, caribou, Clark, Custer, Franklin, Fremont,
Jefferson, Lemhi, Madison, Oneida, Power & Teton counties.

19

Table 6. Average cotton lint harvested areas, yields possible water savings throughachieving expected WUE.
Counties
Harvested Avg. Lint
Water
Regionhectares
Yield
Savings?
(Mg/ha)(ha-m/yr)
Arizona (Upland cotton)
Lapaz
10 033
1.424346
Maricopa
48 752
1.36
18279
Mohave
2283
1.28
909
Pinal
43 285
1.35
15782
Yuma
9291
1.42
3278
Arizona (Pima cotton)
La Paz
1814
1.01
914
Maricopa
7516
0.93
3655
Pinal
14 404
0.91
6854
Yuma
1491
1.12
550
California (Upland cotton)
C. Sac.V.(‘95-99) Colusa/Glenn
2194
1.14
255
S. Sac.V.(‘96-99) Yolo
1076
1.11
160
N. SJV
Merced30 102
1.44
0
1
C. SJV
Madera/Fresno/
195 926
1.44
Tulare13365
2
S. SJV
Kern/ Kings
183 149
1.30
29193
S. Desert3
Riverside
5900
1.35
2151
Low Desert 4
Imperial
4433
1.39
1563
California (Pima cotton)
C. SJV (‘92-99) Fresno
27 287
1.34
0
S. SJV (‘92-99) Kern/ Kings
37 0711.17
3210
1Upland cotton area has decreased ~30% since 1988 while Pima area has tripled since 1992.
2
Upland cotton area has decreased ~50% since 1988 while Pima area has doubled since 1992.
3
Cotton planted area has decreased by a factor of ~2.4 since 1988.

20

List of Figures
Figure 1. Water productivity (value) in the USA and Hong Kong during the 20 th century.
Figure 2. Schematic illustration of the upper and lower basins of the Colorado River.
Figure 3. Y=f(ETc) relationship for alfalfa hay production in the Great Valley, California.
Figure 4. Potential water savings associated with cotto n production based on estimatedand actual water requirements from field trials in Arizona and southern California.
Figure 5. Dependence of Yield/ET c on ETc for hay production in AZ and CA.
Figure 6. Dependence of water value on ETc for hay production in AZ and CA.
Figure 7. Dependence of Yield/ET c on ETc for cotton lint production in AZ and CA.
Figure 8. Dependence of water value on ETc for cotton lint production in AZ and CA.
Figure 9. Dependence of possible water savings on ETc for hay and cotton lint
production in AZ and CA.

21

3
Water Productivity based on GDP ($/m
)
18.00
16.00

USA
HK

1000

12.00

800

10.00
600
8.00
6.00

1990 HK$/m3

1996 US$/m3 iiiii

14.00

1200

400

4.00
200
2.00
0.00
1900

0
1910

1920

1930 1940

1950

1960

1970

1980 1990

2000

Year

Figure 1. Water productivity (value) in the USA and Hong Kong during the 20 th century.

Figure 2. Schematic illustration of the upper and lower basins of the Colorado River.

22

22.0

Yield (Mg/ha) iii

20.0
y = 0.0187x - 5.9143
2
R = 0.7338

18.0
16.0
14.0
12.0
10.0
8.0
6.0
0

200

400

600

800

1000

1200 1400

1600

1800

2000

Estimated ET c = 0.90*ETo
Figure 3. Y=f(ETc) relationship for alfalfa hay production in the Great Valley, California.

Water Savings? (mm) iiiiii

600
y = -x + 1338

CA
AZ

500

2

R =1

400
300

-0.0033xy = 2690.2e2

R = 0.9164

200
100
0
0

100 200 300 400 500 600 700 800 900 1000
Study ETc (mm)Figure 4. Potential water savings associated with cotton production based on estimatedand actual water requirements from field trials in Arizona and southern California.

23

Yield/ETc (kg/ha-mm) iiiiii

18
y = -0.0042x + 17.9

162

R = 0.518

14
12
10
8
6
4
AZ-CA alfalfa

2

CA sudangrass

0
0

200

400

600

800 1000 1200 1400 1600 1800 2000

Estimated ETc (mm)Figure 5. Dependence of Yield/ETc on ETc for hay production in AZ and CA.

3500

IW$ (USD/ha-m) iiiii

y = -0.9281x + 2867.5

3000

2

R = 0.4485

2500
2000
1500
1000
AZ-CA alfalfa
CA sudangrass

500
0
0

200

400

600

800 1000 1200 1400 1600 1800 2000

Estimated ETc (mm)Figure 6. Dependence of water value on ETc for hay production in AZ and CA.

24

LYield/ETc (kg/ha-mm) iiiiii

2
y = -0.0011x + 2.5073

1.8

2

R = 0.6686

1.6
1.4

y = -0.0013x + 2.5051
2

1.2

R = 0.6326

1
0.8
0.6
0.4

upland
pima

0.2
0
0

200

400

600

800

1000

1200

1400

1600

Estimated ETc (mm)Figure 7. Dependence of Yield/ETc on ETc for cotton lint product ion in AZ and CA.

5000
y = -2.9502x + 5343.9

IW$ (USD/ha-m) iiiiii

4500

2

R = 0.8004

4000
y = -3.1909x + 5963.3

3500

2

R = 0.7031

3000
2500
2000
1500
1000

upland
pima

500
0
0

200

400

600

800

1000

1200

1400

1600

Estimated ETc (mm)Figure 8. Dependence of water value on ETc for cotton lint production in AZ and CA.

25

Water savings? (% of ET) iiiiiiiii

60
alfalfasudangrasscotton50

y = 0.0287x - 9.9193
2
R = 0.5372

4030

y = 0.0378x - 17.429
2
R = 0.3342

20
10
0
0

200

400

600

800

1000 1200 1400 1600 1800 2000

Esimated ETc (mm)Figure 9. Dependence of possible water savings on ETc for hay and cotton lint
production in AZ and CA.

26